Observational Astronomy is Gola Sastra. Jyotish Sastra is the study of nine grahas: Sūrya, Chandra, Maṅgala, Budha, Guru, Śukra, Shani and the two chaya grahas, Rahu and Ketu. The English names for these planets are Sun, Moon, Mars, Mercury, Jupiter, Venus, Saturn, Rahu, and Ketu. Although the western world refers to “Planets”, the Vedic term is Graha. Graha comes from the word grahana, which means to eclipse. Rahu is the northern intersection (the north node) and Ketu is the southern intersection (the south node) of the plane of the moon’s orbit around the earth with the plane of the ecliptic. We will learn more about the nodes in subsequent lessons.